Jarren Duran, Jorge Polanco, Aaron Judge and Month-to-Month Consistency

As with many of my articles, Wednesday’s piece on Jarren Duran had its genesis in one of my weekly chats, back in early January. With the Red Sox dealing with a crowded outfield, a reader proposed a trade return for Duran, and in the context of sidestepping the specifics of the deal, I offered a rather curt dismissal of Duran as having had “a pretty meh age-28 season” in 2025. When I received pushback for that bit of reflexive hyperbole — which stood in contrast to the more measured answers I generally give at a notoriously slower pace — I offered a table of his monthly batting splits, and rather than let a debate hijack the chat, I squirreled away the idea of writing more in depth about Duran at a later date.

That date arrived earlier this week, as I caught up with some of the outfielder’s recent comments and other news out of Red Sox camp while diving into his 2025 season. In terms of value, Duran’s fall-off from a 6.8-WAR 2024 season to a 3.9-WAR ’25 campaign produced the second-largest drop in WAR among players with at least 600 plate appearances in both seasons. Duran was still quite valuable — tied for 16th among AL position players in WAR — but not exceptional. “Pretty meh” was obviously an overstatement, but as I noted in the chat, Duran’s above-average offensive production (a 111 wRC+) was driven by one exceptional month that papered over three subpar ones and two others more or less in line with his seasonal numbers:

Duran’s July sticks out like a sore thumb; he didn’t have a slugging percentage within 250 points of it, or a wRC+ within 80 points of it, in any of the other five months. Take his midsummer surge — which included 35 total bases in 35 at-bats against the Twins, Rockies, and Nationals — out of the equation and Duran hit just .247/.320/.405 (98 wRC+) in the other five months.

Small samples being what they are, these things happen all the time in baseball, and if we care to, we can dig through the data to help illuminate why, knowing that random distribution, good or bad luck on batted balls, extremes in the caliber of opponents faced, and arbitrary endpoints all help to explain month-to-month variance. I was much less interested in the whys of Duran’s big July than in the why nots of his whole season when compared to 2024, but even after addressing those at length in the article, the pattern of his production — one big month and five not-so-big ones — stuck with me. How often does something like this happen?

Had I been able to formulate a concise definition of what I sought, I could have asked a colleague with database skills to spit out an answer in a matter of a few minutes. But with only a vague idea, and in the interest of learning by doing, I spent several hours in Excel and with our splits leaderboards. To keep things relatively simple, I maintained focus on overall production (wRC+) instead of a slash stat, such as slugging percentage, or a Statcast-based expected stat, such as xSLG. I settled upon grabbing every hitter-month with at least 75 plate appearances, lumping together March and April as we generally do within our leaderboards. That comes to about 200 hitters per month. I then chose to examine only those players who reached 75 plate appearances in all six months, which left me with 80 hitters out of the 177 who totaled at least 450 plate appearances (75 x 6).

Here I should point out that this is taking an already flattened measure — wRC+ doesn’t tell us how a player reached a given level of production, whether it was thanks to an extreme BABIP or an atypical power burst (or outage) or a sudden inability to hit water while falling out of a boat — and absolutely steamrolling it. While 75 plate appearances was the cutoff, most months featured a few players with at least 120, with Ian Happ maxing out at a major league-high 151 in March and April thanks to the Cubs’ early start in the Tokyo Series against the Dodgers. The Brewers’ William Contreras somehow reached 140 plate appearances in August, the highest total for any month after April. Duran recorded 149 plate appearances in March/April, ranking second to Happ, and he did so without the benefit of a trip to Japan because the Red Sox were the only team to play 32 games before May 1.

So yes, I’m well aware that I’m comparing months where one sample might be twice as large as another, but again, this wasn’t supposed to be rocket surgery, just a fun little spreadsheet full of splits. It’s a good month for exploring such things even when they don’t mean much in the grand scheme.

From there, I tried a few ideas on for size. The most obvious one was to calculate the largest gaps between hitters’ highest monthly wRC+ and their season marks:

That gets to the heart of the matter reasonably well: players who had one big month far above their overall baseline. Duran’s right there with the fourth-highest gap on a list topped by Polanco, whom you may recall excelling while limiting himself to batting only left-handed due to a late-March oblique strain. He slashed .384/.418/.808 with nine homers in just 80 plate appearances (75 as a lefty) in that season-opening stretch.

What about the difference between a player’s best month and his second-best month? I just learned how to find this in Excel! Did you know there are functions called LARGE and SMALL? I was yesterday years old when I discovered that “=LARGE(Table1[@[April]:[Sept]],2)” would tell me a player’s second-highest monthly wRC+. This amused me to an unreasonable degree, because it’s not every day I learn a new spreadsheet trick.

Again, Duran is near the top, with two of the three names above him in the first table also above him in the second. There’s a gap between those four and the next cluster, and a whole lot of crossover between the lists further down; you can tell simply by how few of the players in that table are in bold, recognized upon first mention by our Player Linker.

Now, how about the widest range between best and worst months?

Polanco followed that April feast with a May famine (.139/.205/.208 in 78 PA) while still avoiding most lefties. I extended that table past the usual top 20 to fit Duran; the gap between his red-hot July and his mediocre May put him in a virtual tie for 23rd. (There are decimals attached to these numbers when you export them into spreadsheets, but let’s not split hairs.)

Speaking of famines, note the presence of Harris, whose 11 wRC+ in June (.148/.165/.261 in 92 PA) was the worst month for any player who reached the 75-plate appearance threshold in all six months. He finally heated up in the second half, but things were uncharacteristically grim for awhile. If you’re wondering about who had the worst months at the 75-plate appearance cutoff, Red Sox infielder Kristian Campbell produced a -6 (.134/.184/.171 in 87 PA in May) and Marlins outfielder Dane Myers a -4 (.153/.173/.194 in 75 PA in July), which, yikes; both had their playing time curtailed, with Campbell soon demoted to Triple-A for the balance of the season. Among players who reached the 450-plate appearance threshold, the Rockies’ Brenton Doyle had a 1 wRC+ in June and a 5 wRC+ in September, though he missed the 75-plate appearance cutoff for July, and so he didn’t qualify for further study here. Even the Rockies can take only so much.

Meanwhile, check out Soto and Raleigh, MVP-caliber studs who even in their worst months were still above-average hitters. The same is true for AL MVP Aaron Judge, and as a matter of fact, just 11 hitters who met the 75-plate appearance threshold in all six months had a wRC+ of at least 100 in their worst month:

It’s absolutely remarkable how Judge towers over the field; his worst month — in which the bum hit a pedestrian .253/.388/.579 — was 30 points of wRC+ better than anybody else’s worst month, and higher than the season wRC+ marks of all but four batting title qualifiers (Ohtani, Raleigh, Soto, and George Springer). Duran didn’t make the cut for this table, but it’s worth noting that his 87 wRC+ from May still put him in a virtual tie for the 19th-best worst month — in other words, a pretty respectable floor.

I crunched the numbers in a few other ways. Want to know which hitters came back to earth the hardest after fantastic starts? Here’s a table of the largest gaps between April wRC+ and season marks at both extremes, including the players who dug themselves out of early holes:

There’s Polanco again, and Judge wrapping up an absolutely monster 365-day stretch. At the other end of the spectrum, remember all that fretting about Soto’s slow start in Queens? It turns out the dude did not forget how to hit, and finished with a wRC+ within two points of his career mark. Adell’s presence caught my eye here; he looked ready to be written off for good after a dreadful April, but half a decade after being a top-10 prospect, he finally turned in a cromulent major league season.

Now for the flip side of that table, showing the hitters whose final month produced similar extremes:

Arraez, Bell, and Betts nosed themselves over the 100 wRC+ line thanks to hot Septembers. Olson capped a nice bounce-back year after a comparatively subpar 2024. Naylor’s late surge carried over into a star turn in the postseason. And here we have even more Polanco, who ended up with an impressive set of bookends to his season. Judge’s turning up again is wild, as well. He bracketed his season with a 251 wRC+ in March/April and a 241 wRC+ in September; he also hit for a 229 wRC+ in May, 154 in June (noted above), 173 in July, and 157 in August, in case you were wondering.

Another thing we can do with this spreadsheet is figure out the most and least consistent hitters from month to month based upon the standard deviations of their wRC+. First, the ones with the lowest standard deviations across the six-month sample, the most consistent overall:

Not surprisingly, a lot of those players are within an infielder’s underhand flip of league average, which is only so interesting. More impressive are the stars who were particularly consistent from month to month. In an effort to tease that out, here’s a second version of the list, limited to hitters with a season wRC+ of 120 or higher:

That’s pretty cool, especially the hitters who didn’t have a single month below 100. I’m repeating information from the Best Worst Month table, but who would have expected Suzuki and Grisham to share such a distinction with the likes of Guerrero, Witt, and Ohtani? Who would have even noticed, if not for this little exercise?

On the other side of the ledger, here are the hitters with the most volatile performances from month to month. You won’t be surprised by who tops the list:

It’s funny to see Polanco, whom the Mets signed to play first base, in a table just above Alonso, the man he’s charged with replacing — a rough reminder that Polar Bear Pete went ice cold for a couple of months even in the summer, though aside from his aforementioned 213 wRC+ in March/April, his monthly performances were completely out of sync with those of the Mets, who were above .500 in his subpar months and below .500 in his good ones. Again, I extended the table to include Duran, whose standard deviation in wRC+ was nonetheless closer to landing him on the first “Steady Eddie” list — 14 points higher than J-Rod — than to topping this one.

There’s a lot more to analyze with regards to any of these players’ seasons than just wRC+, myriad reasons why they might have gone on hot streaks or slumps. This exercise did answer my question with regards to Duran — yes, having just one outstanding month as he did was unusual, and the gap between that month and the rest of his line rather extreme, but even at his worst he wasn’t truly terrible — and it helped me appreciate the ups and downs of so many other players’ seasons, too.